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Mapping of Functional Groups in Metal-Organic Frameworks

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Science  23 Aug 2013:
Vol. 341, Issue 6148, pp. 882-885
DOI: 10.1126/science.1238339

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Mapping Molecular Linkers

In metal-organic framework compounds, inorganic centers (metal atoms or clusters) are linked by bidentate organic groups. Normally, the same group is used throughout the structure, but recently, synthesis with linkers bearing different functional groups has produced well-defined materials. Kong et al. (p. 882, published online 25 July) combined solid-state nuclear magnetic resonance and molecular simulations to map the distributions of linkers in these materials as random, well-mixed, or clustered.

Abstract

We determined the heterogeneous mesoscale spatial apportionment of functional groups in a series of multivariate metal-organic frameworks (MTV-MOF-5) containing BDC (1,4-benzenedicarboxylate) linkers with different functional groups—B (BDC-NH2), E (BDC-NO2), F [(BDC-(CH3)2], H [BDC-(OC3H5)2], and I [BDC-(OC7H7)2]—using solid-state nuclear magnetic resonance measurements combined with molecular simulations. Our analysis reveals that these methods discern between random (EF), alternating (EI and EHI), and various cluster (BF) forms of functional group apportionments. This combined synthetic, characterization, and computational approach predicts the adsorptive properties of crystalline MTV-MOF systems. This methodology, developed in the context of ordered frameworks, is a first step in resolving the more general problem of spatial disorder in other ordered materials, including mesoporous materials, functionalized polymers, and defect distributions within crystalline solids.

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